1. Field of the Invention
The present invention relates to a vehicle wiper controller for controlling a wiper by accurately detecting a rainfall state.
2. Description of the Related Art
A raindrop sensor formed using the optical technique is known as being employed in a vehicle wiper controller for controlling a wiper.
In the generally employed raindrop sensor using the optical technique, light rays irradiated from a light-emitting element reflect on a detection surface, and the light-receiving element receives the reflecting light to detect raindrops. Specifically, when water is adhered onto the detection surface, the light reflecting condition on the detection surface changes, and accordingly, the amount of light received by the light-receiving element also changes. The raindrops adhered onto the detection surface may be detected based on the change in the amount of light received by the light-receiving element.
Various methods for detecting the raindrops adhered onto the detection surface based on the change in the amount of received light have been proposed. For example, the method for detecting the raindrops in comparison with the reference value is disclosed in Japanese Unexamined Patent Application Publication No. 61-37560, and the method for detecting the raindrops by accumulating outputs of the light-receiving element is disclosed in Japanese Patent Application Laid-Open No. 4-349053.
Because of a mount location and a small raindrop detection area, the raindrop sensor of the aforementioned type is unlikely to provide the stable detection result.
The resultant output values of the raindrop sensor may differ even in the similar rainfall state. The direct reflection of the detection result of the raindrop sensor in the wiper operation control may fail to appropriately control the wiper. The detection result of the raindrop sensor is required to be monitored for a predetermined period to determine adequacy of the detection results for the purpose of controlling the wiper operation. This may prolong the time for feedback of the detection results to the wiper control.
In the aforementioned case, it is difficult to detect sharp change in the rainfall state so as to be reflected in the wiper control. When the vehicle goes into the tunnel while operating the wiper at high speeds under the heavy rain, the operation for switching the operation speed of the wiper from high to low, or stopping the wiper operation cannot be immediately performed. The aforementioned wiper operation will make the driver feel unpleasant.